1. Field of the Invention
The present invention relates to a method for producing a semiconductor device using a technique for transferring thin-film elements between substrates.
2. Description of the Related Art
It is sometimes desirable to use plastic substrates for substrates in order to lower costs and prevent breakage caused by flaking or deformation in semiconductor devices such as liquid crystal display (LCD) panels and electroluminescence (EL) displays.
However, processes involving elevated temperatures are employed in the production of thin-film transistors which are used in such panel types of displays, yet circuit elements such as EL elements and plastic substrates are susceptible to such elevated temperatures.
The Applicant has proposed a transfer technique for producing semiconductor application devices by forming a semiconductor device on a heat-resistant base substrate using a conventional semiconductor-forming technique which includes a high-temperature process, then peeling the element-forming film (layer) with which the semiconductor device is formed from the substrate, and laminating the film to a plastic substrate. The details are described, for example, in xe2x80x9cMethod of Peelingxe2x80x9d in Japanese Unexamined Patent Applications (Kokai) 10-125929, 10-125930, and 10-125931.
Semiconductor devices produced with the use of the aforementioned method of peeling include structures such as thin-film transistors and similar element-forming layers, adhesive layers to which an adhesive has been applied, and plastic substrates, but the film thickness of the adhesive is about 10 to 100 xcexcm, and the thickness of the substrate is about 50 to 500 xcexcm, resulting in a semiconductor device with a relatively high overall thickness. The adhesive must also allow both the element-forming layer and substrate to adhere (be joined). Furthermore, differences in the coefficient of thermal expansion between the layers including the adhesive can cause warping and cracks, possibly lowering the heat resistance (reliability) of semiconductor application devices.
An object of the present invention is thus to provide a semiconductor device without an adhesive layer for semiconductor devices which are produced using a technique for peeling an element-forming layer from a heat-resistant substrate to transfer the layer to another substrate.
Another object of the present invention is to produce a thinner semiconductor device from a semiconductor device produced by a manufacturing process involving the use of a separation and transfer technique.
Another object of the present invention is to produce a semiconductor device with better heat resistance from a semiconductor device produced by a manufacturing process involving the use of a peeling and transfer technique.
A first method for transferring an element in the present invention in order to achieve the aforementioned objects comprises the steps of forming a peeling layer in which the bonding force weakens under certain conditions on an element-forming substrate for forming an element; forming an element-forming layer including an element on the peeling layer; joining the element-forming layer by means of a dissolvable bonding layer to a temporary transfer substrate; weakening the bonding force of the peeling layer to peel the element-forming layer from the element-forming substrate, and moving the layer to the temporary transfer substrate side; applying resin onto the element-forming layer which has been moved to the temporary transfer substrate, and curing the resin to form a transfer substrate; and dissolving the bonding layer to peel the temporary transfer substrate from the transfer substrate.
Such a structure can be produced to join the transfer substrate and the element-forming substrate without an adhesive layer between them, thus allowing a thinner semiconductor device to be formed. Because the conventional three-layer structure involving an element-forming layer (such as a thin-film transistor), an adhesive layer (adhesive), and a transfer substrate (plastic substrate) can be converted to a two-layer structure (element-forming layer, transfer substrate), it is easier to ensure that the coefficients of thermal expansion of the layers are closer together in order to minimize warpage and cracks.
A second method for transferring an element in the present invention comprises the steps of forming a peeling layer in which the bonding force weakens under certain conditions on an element-forming substrate for forming an element; forming an element-forming layer including an element on the peeling layer; applying resin onto the element-forming layer, and curing the resin to form a transfer substrate; and weakening the bonding force of the peeling layer to peel the element-forming substrate from the element-forming layer, and moving the element-forming layer to the transfer substrate side.
Such a structure can be produced to join the transfer substrate and the element-forming substrate without an adhesive layer between them, thus allowing a thinner semiconductor device to be formed. In this case, the element-forming layer can be formed with fewer steps.
The present invention can also further comprise the step of opening contact holes in the element-forming layer to form a wired layer or electrode layer, and can thus include elements and wiring/electrodes or the like on the inverted element-forming layer.
In the present invention, xe2x80x9celementxe2x80x9d includes TFT, diodes, resistors, inductors, capacitors, and other unit elements, whether active or passive elements, of any structure, shape, or size.
In the present invention, xe2x80x9cpeeling layerxe2x80x9d is preferably a peeling layer in which the bonding force between atoms or molecules is lost or diminished when irradiated by light such as laser beams, resulting in peeling, and is made of a material that undergoes such peeling.
The peeling layer is preferably made of at least one material selected from the group consisting of amorphous silicon, silicon nitride, and metals, and may also be a multilayered film made of a combination thereof. This makes it easier to bring about separation in the peeling layer and in the interface between the peeling layer and adjacent layers. For example, silicone nitride contains nitrogen, and the nitrogen separated when irradiated with light rays, weakening the bonding force between molecules.
The peeling layer preferably includes hydrogen. the hydrogen will thus separate (become a gas) when irradiated with light rays, weakening the bonding force between molecules.
The bonding layer is preferably a liquid dissolvable adhesive such as a water-soluble adhesive, which dissolves away when washed with water.
The present invention also relates to a method for producing an element, comprising the steps in the aforementioned method for transferring an element. It also relates to an integrated circuit produced by such a transfer method.
In the present invention, xe2x80x9cintegrated circuitxe2x80x9d refers to a circuit in which elements and wiring are integrated to perform a certain function. For example, xe2x80x9cintegrated circuitxe2x80x9d refers to circuits comprising a plurality of active elements (such as thin-film transistors) or passive elements (such as resistors and capacitors) formed on the same substrate (in the present invention, the final transfer substrate) by means of a chemical technique such as ion implantation, diffusion, or photoetching. Such circuits are classified, depending on the degree of integration, into small-scale integrated circuits (such as NAND circuits and NOR circuits), medium-scale integrated circuits (such as counters and resistor circuits), and large-scale integrated circuits (such as memory, microprocessors, and DSP).
The present invention also relates to circuit boards produced by the aforementioned method for transferring an element. Examples include a circuit board comprising elements disposed in a plurality of two-dimensionally disposed pixel electrodes, such as an active matrix substrate, which has been produced by the aforementioned method for transferring an element.
The present invention also relates to an electro-optical device comprising such a circuit board.
As used here, xe2x80x9celectro-optical devicexe2x80x9d generally refers to devices with electro-optical elements which emit light or modify light from elsewhere by means of electrical action, and include both those that emit light themselves and those that control the transmission of light from elsewhere. Examples include active matrix types of displays equipped with electro-optical elements such as liquid crystal elements, electrophoresis elements, EL (electroluminescence) elements, and electron-emitting elements that emit light when electrons produced by the application of an electrical field come into contact with a light-emitting board. Such devices are not limited to these, of course.
The present invention also relate to an electronic appliance produced by the aforementioned method for transferring an element.
As used here, xe2x80x9celectronic appliancexe2x80x9d generally refers to devices that have a certain function as a result of a combination of a plurality of elements or circuits. Although the structure is not particularly limited, examples include IC cards, cellular telephones, video cameras, personal computers, head-mounted displays, rear or front projectors, as well as FAX machines with display functions, digital camera finders, portable TV, DSP devices, PDA, electronic organizers, electronic signs, and displays for advertising announcements.